/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <fcntl.h>

#include <sys/stat.h>

#include <syslog.h>

#include <unistd.h>

#ifdef ARCH_MIPS

#include <asm/sgidefs.h>

#endif

#include "alloc-util.h"

#include "base-filesystem.h"

#include "errno-util.h"

#include "fd-util.h"

#include "log.h"

#include "nulstr-util.h"

#include "path-util.h"

#include "umask-util.h"

#include "user-util.h"

typedef enum BaseFilesystemFlags {

        BASE_FILESYSTEM_IGNORE_ON_FAILURE = 1 << 0,

        BASE_FILESYSTEM_EMPTY_MARKER      = 1 << 1, /* If this is missing, then we are booting on an empty filesystem - see comment below */

        BASE_FILESYSTEM_EMPTY_ONLY        = 1 << 2, /* If booting on an empty filesystem create this, otherwise skip it - see comment below */

} BaseFilesystemFlags;

typedef struct BaseFilesystem {

        const char *dir;      /* directory or symlink to create */

        mode_t mode;

        const char *target;   /* if non-NULL create as symlink to this target */

        const char *exists;   /* conditionalize this entry on existence of this file */

        BaseFilesystemFlags flags; /* various modifiers for behaviour on creation */

} BaseFilesystem;

/* Note that as entries are processed in order, entries with BASE_FILESYSTEM_EMPTY_MARKER must be listed

 * before entries with BASE_FILESYSTEM_EMPTY_ONLY. */

static const BaseFilesystem table[] = {

        { "bin",      0, "usr/bin\0",                  NULL,                        BASE_FILESYSTEM_EMPTY_MARKER      },

        { "lib",      0, "usr/lib\0",                  NULL,                        BASE_FILESYSTEM_EMPTY_MARKER      },

        { "root",  0750, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },

        { "sbin",     0, "usr/sbin\0",                 NULL,                        BASE_FILESYSTEM_EMPTY_MARKER      },

        { "usr",   0755, NULL,                         NULL },

        { "var",   0755, NULL,                         NULL },

        { "etc",   0755, NULL,                         NULL },

        { "proc",  0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },

        { "sys",   0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },

        { "dev",   0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },

        { "run",   0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },

        /* We don't add /tmp/ here for now (even though it's necessary for regular operation), because we

         * want to support both cases where /tmp/ is a mount of its own (in which case we probably should set

         * the mode to 1555, to indicate that no one should write to it, not even root) and when it's part of

         * the rootfs (in which case we should set mode 1777), and we simply don't know what's right. */

        /* Various architecture ABIs define the path to the dynamic loader via the /lib64/ subdirectory of

         * the root directory. When booting from an otherwise empty root file system (where only /usr/ has

         * been mounted into) it is thus necessary to create a symlink pointing to the right subdirectory of

         * /usr/ first — otherwise we couldn't invoke any dynamic binary. Let's detect this case here, and

         * create the symlink as needed should it be missing. We prefer doing this consistently with Debian's

         * multiarch logic, but support Fedora-style and Arch-style multilib too. */

#if defined(__aarch64__)

        /* aarch64 ELF ABI actually says dynamic loader is in /lib/, but Fedora puts it in /lib64/ anyway and

         * just symlinks /lib/ld-linux-aarch64.so.1 to ../lib64/ld-linux-aarch64.so.1. For this to work

         * correctly, /lib64/ must be symlinked to /usr/lib64/. On the flip side, we must not create /lib64/

         * on Debian and derivatives as they expect the target to be different from what Fedora et al. use,

         * which is problematic for example when nspawn from some other distribution boots a Debian

         * container with only /usr/, so we only create this symlink when at least one other symlink is

         * missing, and let the image builder/package manager worry about not creating incomplete persistent

         * filesystem hierarchies instead. The key purpose of this code is to ensure we can bring up a system

         * with a volatile root filesystem after all. */

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-linux-aarch64.so.1",       BASE_FILESYSTEM_EMPTY_ONLY        },

#  define KNOW_LIB64_DIRS 1

#elif defined(__alpha__)

#elif defined(__arc__) || defined(__tilegx__)

#elif defined(__arm__)

        /* No /lib64 on arm. The linker is /lib/ld-linux-armhf.so.3. */

#  define KNOW_LIB64_DIRS 1

#elif defined(__i386__) || defined(__x86_64__)

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-linux-x86-64.so.2" },

#  define KNOW_LIB64_DIRS 1

#elif defined(__ia64__)

#elif defined(__loongarch_lp64)

#  define KNOW_LIB64_DIRS 1

#  if defined(__loongarch_double_float)

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-linux-loongarch-lp64d.so.1" },

#  elif defined(__loongarch_single_float)

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-linux-loongarch-lp64f.so.1" },

#  elif defined(__loongarch_soft_float)

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-linux-loongarch-lp64s.so.1" },

#  else

#    error "Unknown LoongArch ABI"

#  endif

#elif defined(__m68k__)

        /* No link needed. */

#  define KNOW_LIB64_DIRS 1

#elif defined(_MIPS_SIM)

#  if _MIPS_SIM == _MIPS_SIM_ABI32

#  elif _MIPS_SIM == _MIPS_SIM_NABI32

#  elif _MIPS_SIM == _MIPS_SIM_ABI64

#  else

#    error "Unknown MIPS ABI"

#  endif

#elif defined(__powerpc__)

#  if defined(__PPC64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld64.so.2" },

#    define KNOW_LIB64_DIRS 1

#  elif defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__

        /* powerpc64-linux-gnu */

#  else

        /* powerpc-linux-gnu */

#  endif

#elif defined(__riscv)

#  if __riscv_xlen == 32

#  elif __riscv_xlen == 64

        /* Same situation as for aarch64 */

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-linux-riscv64-lp64d.so.1", BASE_FILESYSTEM_EMPTY_ONLY        },

#    define KNOW_LIB64_DIRS 1

#  else

#    error "Unknown RISC-V ABI"

#  endif

#elif defined(__s390x__)

        /* Same situation as for aarch64 */

        { "lib64",    0, "usr/lib64\0"

                         "usr/lib\0",                "ld-lsb-s390x.so.3",           BASE_FILESYSTEM_EMPTY_ONLY        },

#    define KNOW_LIB64_DIRS 1

#elif defined(__s390__)

        /* s390-linux-gnu */

#elif defined(__sparc__)

#endif

        /* gcc doesn't allow pragma to be used within constructs, hence log about this separately below */

};

#ifndef KNOW_LIB64_DIRS

#  pragma message "Please add an entry above specifying whether your architecture uses /lib64/, /lib32/, or no such links."

#endif

int base_filesystem_create_fd(int fd, const char *root, uid_t uid, gid_t gid) {

        bool empty_fs = false;

        int r;

        assert(fd >= 0);

        assert(root);

        /* The "root" parameter is decoration only – it's only used as part of log messages */

        FOREACH_ELEMENT(i, table) {

                if (FLAGS_SET(i->flags, BASE_FILESYSTEM_EMPTY_ONLY) && !empty_fs)

                        continue;

                if (faccessat(fd, i->dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)

                        continue;

                if (FLAGS_SET(i->flags, BASE_FILESYSTEM_EMPTY_MARKER))

                        empty_fs = true;

                if (i->target) { /* Create as symlink? */

                        const char *target = NULL;

                        /* check if one of the targets exists */

                        NULSTR_FOREACH(s, i->target) {

                                if (faccessat(fd, s, F_OK, AT_SYMLINK_NOFOLLOW) < 0)

                                        continue;

                                /* check if a specific file exists at the target path */

                                if (i->exists) {

                                        _cleanup_free_ char *p = NULL;

                                        p = path_join(s, i->exists);

                                        if (!p)

                                                return log_oom();

                                        if (faccessat(fd, p, F_OK, AT_SYMLINK_NOFOLLOW) < 0)

                                                continue;

                                }

                                target = s;

                                break;

                        }

                        if (!target)

                                continue;

                        r = RET_NERRNO(symlinkat(target, fd, i->dir));

                } else {

                        /* Create as directory. */

                        WITH_UMASK(0000)

                                r = RET_NERRNO(mkdirat(fd, i->dir, i->mode));

                }

                if (r < 0) {

                        bool ignore = IN_SET(r, -EEXIST, -EROFS) || FLAGS_SET(i->flags, BASE_FILESYSTEM_IGNORE_ON_FAILURE);

                        log_full_errno(ignore ? LOG_DEBUG : LOG_ERR, r,

                                       "Failed to create %s/%s: %m", root, i->dir);

                        if (ignore)

                                continue;

                        return r;

                }

                if (uid_is_valid(uid) || gid_is_valid(gid))

                        if (fchownat(fd, i->dir, uid, gid, AT_SYMLINK_NOFOLLOW) < 0)

                                return log_error_errno(errno, "Failed to chown %s/%s: %m", root, i->dir);

        }

        return 0;

}

int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {

        _cleanup_close_ int fd = -EBADF;

        fd = open(ASSERT_PTR(root), O_DIRECTORY|O_CLOEXEC);

        if (fd < 0)

                return log_error_errno(errno, "Failed to open root file system: %m");

        return base_filesystem_create_fd(fd, root, uid, gid);

}